Windows only: MediaMonkey manages your music collection like no other program. It helps you organize your audio files, edit tags, and easily retrieve missing album art. It can rip CDs to any number of formats (including cult faves like FLAC and OGG), convert existing audio files to any number of formats, normalize volume levels across all your tracks, and much more.

It even lets you sync with portable players like the iPod and Creative Zen Vision. In short, this is one of my all-time favorite programs, and it's free! (The $19.95 Gold version adds a few desirable features, like automatic library updating.) Its only Achilles' heel is lack of support for protected AAC files and WMA DRM 10 (though it does support up to version 9). But it's still a killer freebie for anyone looking to get their music library in order.